Time limit contactor



Nov. 3, 1942.

R. B. IMME L TIME LIMIT CONTACTORS Filed July 12, 1940 iii/ll iii/"17) a hwy MS M '11 INVENTOR E040/L5fmme/ WITNESSES:

ATTORNEY Patented Nov. 3., 1942 TIME LIMIT CONTAGTOR Ralph B. Immel, Wilkinsburg, Pa., a'ssig'nor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 12, 1940, Serial No. 345,064

4 Claims.

My invention relates, generally, to electromagnetic devices and more particularly to direct current actuated time limit contactors.

In the design and construction of electromagnetic devices or contactors, it is often desirable to provide for a long yet predetermined delay in operation of the device. Suitable devices of this character are shown and described in the patents to Schaelchlin, et al. No. 1,979,709 issued November 6, 1934, and entitled Time limit contactor, and to Cook, No. 1,753,983, issued April 8, 1930, and entitled Control system.

Since my invention is an improvement on this particular type of contactors, shown in these patents, I am hereinafter redescribing so much of the contactor shown in detail in the Schaelchlin, et al. patent as is thought necessary to fully describe my contribution to the art without having to refer to such prior patent.

One object of my invention is to make an electromagnetic time limit device more accurate as to the measurement of time and more reliable so that the same operation may be expected even though the operating conditions may vary.

Another object of my invention is to prevent the sticking of the armature of a direct current electromagnetic time-limit device upon deenergization of the armature actuating coil by either opening the coil circuit or short-circuiting the coil.

A still other object of my invention is to reliably increase the time rating of an electromagnetic device.

It is also an: object of my invention to make the operation of a direct current electromagnetic time-limit device less sensitive to changes of operating conditions.

Other objects and advantages of my invention will become more apparent from a study of the following specification and the drawing accompanying the specification and made part hereof.

In the drawing:

Figure l is a view in side elevation, partly in section, of a time-limit electromagnetic contactor constructed in accordance to my invention;

Fig. 2 is a view of the core and coils only looking in the direction indicated by section lines II-II of Fig. 1;

Fig. 3 is a view of a modification of my invention showing the armature only viewed from the side of the armature coacting with the core;

Fi 4 is a front elevational view of the contactor illustrated in Fig. l and Fig. 5 shows a number of curves which demontromagnetic device constructed in accordance with my invention.

Referring now to the drawing, the electromagnetic time limit device, or Timetactor, illustrated, comprises a frame of magnetic material,

in which a core 31 also of magnetic material is mounted. The core member 3| may be mounted in any suitable manner and in this particular showing a bolt 32, cooperating with the frame 30 and the supporting panel 33 and having threaded engagement with the core, is utilized. The core member is provided with a horizontal groove I00 and a vertical groove Illl. The purpose of these grooves will become apparent later. Extending substantially parallel to the core member 3! is a horizontal armature supporting portion of frame 30 which, in this instance, is constructed to be substantially integral with the frame 30.

An armature 34 is mounted on the fram 30 and is disposed in alignment with the core 3|. To mount the armature for oscillatory movement, a notch 36 is provided at the end of the horizontal portion of frame 30. In the construction illustrated, the notch 36 is provided at the junction of the end portion of frame 30 and a plate 35 is mounted on top of the frame and extending a short distance beyond the end of the frame.

The simplest type of armature that is suitable for this electromagnetic time limit device is a metal plate which is cut square at the end, or preferably cut by planes forming an acute angle at one edge, as 31, of the end of the armature adjacent the end of the frame 30. Further, to provide for a free pivotal movement of the armature when mounted in the notch 36, the walls defining the notch should be spaced at an angle greater than a right angle. The size of the angle of the notch as well as the size of the acute angle at the upper end of the armature will be determined by the desired angle of swing of the armature. In this embodiment of my invention, to make the notch of the desirable angular extent, the plate 35 is bent upwardly at a point near the upper right-hand end of the frame 30.

It will be readily understood that a suificient and free angular motion of the armature may be obtained if the angle of the notch 36 is made slightly greater than the sum of the angle of movement and the acute angle at the knife edge of the armature coacting with the notch 36. I

In order that the armature may be readily mounted, removed and replaced, a rectangular notch 38 is cut in the projecting bent portion of the plate 35. In cutting the notch, the plate 35 strate the characteristics possessed by the elec- 55. is cut at two places to form a tongue portion 39 which is bent upwardly much more than the end portion of plate 35 forming, in part, the notch 36. As shown, a bracket 40 is mounted on the armature and provided with an extension or tongue 4| which extends through the notch 38.

It is not essential that the core be provided with grooves because I can obtain the advantages hereinafter pointed out by providing the armature with grooves I02 and I 03 disposed at right angles to each other and at the region or surface coacting with the end of the core.

The upper tongue 39, which is integral with plate 35, is provided with a slot 42, extending inwardly from the end, for receiving a bolt 43, while the tongue 4! has an opening through which the bolt extends. A spring 45 is mounted on the bolt 43 and is disposed to bias the armature 34 counter-clockwise about the knife edge 31. In this manner, the armature is retained in position, the tongue 4| engages the two sides of the notch 38 to prevent lateral movement, While the spring 45 biases it upwardly into the notch 36.

The armature may be readily removed by con pressing the spring 45 and forcing the bolt 43 upwardly and out of slot 42.

As shown, the bolt 43 is provided with an adjustable nut 45 whereby any desired spring tension may be applied to the armature. The armature is provided with one main contact member 26 pivotally mounted at 41 on the lever 48. A spring 49 biases the contact member in such a direction as to firmly press the upper end of the lever 48 against the bracket 45.

In the showing in Fig. 1, the main coil H is assumed to be energized, thus holding the armature firmly against the armature receiving surface 60.

The core 3| is provided with an armature receiving face 60. As already suggested, the armature face 60 is provided with a horizontal groove I and a vertical groove lill. These grooves are of a predetermined width and a predetermined depth. For each type of electromagnetic device there is a practical width and optimum depth for these grooves. Particular dimensions with a given electromagetic device will be discussed hereinafter. It should be remembered, however, that my contribution is not limited to the particular type of electromagnetic device herein described but is applicable to any direct current time limit device. A copper sleeve 23 is mounted directly on the core. This sleeve need not necessarily. be of copper but may be silver, aluminum, or any other material having a relatively low resistance value, and of such properties that currents are induced therein when the magnetic flux threading the sleeve, i. e., the flux in the core 3|, is varied.

To actuate the armature 34, a main magnetizing coil H is mounted on the sleeve 23. As will be readily understood, this coil ll may be constructed to have any desired number of turns of suitable conductors, which will depend on operating conditions to be met.

As shown, a neutralizing coil 5 is mounted on the magnetizing coil. This coil is so constructed, arranged and energized as to oppose the magnetic effect of the magnetizing coil Ii. The size of the conductor, the degree of energization in operation, and the number of turns provided in the coil 5, will depend upon the main actuating coil II and the manner in which it is desired to dissipate the residual magnetism or preferably the rate at which it is desired to dissipate the residual magnetism that may, in the absence of the neutralizing coil, be retained by the core 3| during the operation of the contactor.

A clearer picture of the advantages of my contribution Will probably be had from a more detailed discusssion of the operation of direct current electromagnetic time limit devices as heretofore known and then an operation of my contribution.

The time-limit device herein described, when not provided with the grooves I00 and |S-l (or I02 and IE3), is too sensitive to voltage variations of the supply. Further, attendants have the habit of decreasing the compression of spring 55 to get a longer time constant. Then if the armature sticks, either because of the spring compression adjustment made or because of other reasons, even when no spring adjustment has been made, an attendant frequently increases the current in the neutralizing coil to dissipate the residual magnetism, as he theorizes, not realizing that the neutralizing coil may be responsible for the offending action. Naturally, the are mature now still sticks. The attendant may now try increasing the compression of spring 45 by tightening nut 46. To be sure the device again becomes operative but the time constant may become very low-often may become uselessly low.

Once the attendant has started making adjustments all the novel, useful and valuable results the electromagnetic devices devised by Schaelchlin, et al. and Cook can and do accomplish may be lost.

One general object of my invention is thus to make direct current electromagnetic devices less critical in operating characteristics without affecting their other novel results.

To more clearly understand what I have generally described in the three paragraphs just preceding, reference should be had to Fig. 5.

Without the grooves, for a given spring adjustment and a given neutralizing coil current, the flux, over one portion of the area of the core face coacting with the armature, decays as indicated by curve A, whereas over other portions of the area of the core coacting with the armature, the flux decays as indicated by curves B, C, etc. to N, respectively, assuming N represents the curve showing the slowest decay. Curve N, it may logically, and I believe correctly be assumed, will thus determine the maximum operating time that may be obtained for the contacts under given conditions of spring and current adjustments.

As the represented by curve A becomes zero, the neutralizing coil, for the correctly adjusted neutralizing coil current builds up armature attracting flux along curve 0. If the armature is to be released, the flux 0 must become equal to the force X of the spring 45 subsequent to the time N has decreased below force X. This means the armature will be released at time t2. If the spring compression is decreased, X decreases and the armature is not released at a1l-- it sticks. If the spring compression is increased t2 rapidly decreases.

If on the other hand, the voltage on the neutralizing coil increases either because the attendant increases the voltage to eliminate the sticking action or because of a voltage increase by reason of normal voltage variations of the circuit, curve A becomes curve A and N and 0 become N and 0, respectively. This is so because a higher voltage causes the flow of a higher neutralizing current and thus causes a more rapid decay of the flux in the magnetic circuit. To now prevent sticking the compression of the spring would have to be adjusted to force y and the time limit woud be t1. As a matter of fact, where voltage fluctuations of a supply are present, which is usually the case in industrial applications, the spring force must be adjusted at substantially the value 1 and in consequence a time constant no greater than subst antially t'i is ever obtained. Under favorable conditions the time limit may vary from h to 262.

With my grooves the flux distribution over the core face is more uniform. Also, there are only very low eddy currents in the core face to help produce holding flux. The flux decay thus follows a single curve, or substantially sharp line, and tests with my device show that this single curve substantially follows curve N. I shall, therefore, use curve N to illustrate what goes on when the grooves are used.

The flux decays along N and as it passes through zero at P the neutralizing coil immediately begins to build up flux along Q. If there is a sufiicient rise in voltage on the neutralizing coil the curve N becomes N and curve Q becomes Q. The spring force may thus safely be adjusted at value 2 and in consequence the relay will always operate, or release its armature at time t3.

One of the considerable advantages of my contribution is that the relay may be operated with high neutralizing ampere turns and a weak spring adjustment. The relay will not stick and the neutralizing ampere turns may even be increased nearly up to the point where the neutralizing winding itself picks up the relay. My device has been reduced to practice and the novel results hereinbefore pointed out have been obtained.

In my investigation I used a standard electromagnetic device, of the type disclosed and claimed by Cook and Schaelchlin, et al., which caused its armature to stick at rather low neutralizing current, that is, it showed exceptionally critical performance. This device, having a size, or rating, substantially twice the scale size of the showing in Fig. l, I provided with one horizontal slot of an inch wide and deep. The slot improved the operation of the device and the armature would stick only at a considerably higher minimum value of neutralizing ampere turns than the minimum value of neutralizing ampere turns that would cause the armature to stick when no slots were used in the core face. The slot was progressively cut h of an inch deeper until a depth of A of an inch was attained and the device tested after each cut. This modification made a great improvement in the operation; however, it did not prevent sticking at the very high neutralizing currents. A slot of 1 of an inch wide and A of an inch deep was then cut vertically in the core face and sticking was prevented entirely. The width of 1 inch was merely selected because narrower scoring tools are expensive and narrower cuts are expensive to make. As a matter of fact, the width should be as small as possible. The slots of the least width are best. a

Increasing the depth of the grooves beyond of an inch and the width to more than of an inch does not materially further improve the operation.

Other devices of the same rating and of different rating were tested with the grooves and the same novel and useful results were obtained in each case.

The dimensions of the grooves are,

of course, merely illustrative; For larger devices, the widthsand depths should bedifierent than here given but ,in general there is an optimum depth of a groove for each size.

The core face is the most convenient place to mill the grooves but the grooves may also be placed on the armature surface coacting with the core as shown in Fig. 3.

My contribution, though it may seem a plain and simple one in character, has nevertheless been found to be a very valuable one and I, therefore, do not wish to be limited to the specific showing made but wish to be limited only by the scope of the claims hereto appended.

I claim as my invention:

1. In an electromagnetic inductive time-limit device, in combination, a core member, an armature disposed to coact with said core member, said core member having an armature engaging face provided with at least one transverse groove in its face to divide the face into at least two portions, means for biasing said armature away from said core member, a coil for causing a magnetic flux in said core member, a second coil for dissipating the flux of said first named coil when the first named coil is deenergized, and a lowresistance closed circuit inductively related to said coils adapted in coaction with said coils and groove to delay and fix the time of dissipation of the magnetic flux so that the flux decay is at substantially the same rate over each of the portions into which the face is divided by said groove.

2. In an electromagnetic inductive time-limit device, in combination, a magnetic circuit comprising a solid iron frame, a solid iron core member, a solid iron armature member coacting with the core member, a pair of right angularly disposed relatively narrow and shallow grooves disposed in the surface of the core member at the region of coaction of the armature member to divide said region into a plurality of portions, means for producing a magnetic flux in said circuit, means for decreasing the rate of decay of said magnetic flux when said means for producing the flux are rendered ineffective, and means, coacting with the grooves, for effecting a substantially uniform like low rate or flux decay over each of the said portions of the core member at the region of coaction with the armature member.

3. In an electromagnetic time-limit device, in combination, a core member provided with a pair of grooves at one end and disposed at right angles to each other to thus divide the end into four areas, an armature coacting with the grooved surface of the core, a spring for biasing the armature to a predetermined position, a coil for magnetizing the core member to effect the operation of the armature against its bias, control means for decreasing the rate of dissipation of the magnetic flux in the core member when the coil is deenergized, and a neutralizing coil, coacting with said grooves and said control means, disposed on said core member to effect substantially the same rate of flux decay over each of the said four areas from a maximum energized condition of the core member to the armature releasing value of energization of the core member, thereby to obtain a positive and unvarying action of the armature at a selected time during the process of dissipation of the residual magnetism.

4. In an electromagnetic inductive time-limit device. in combination, an armature, a core energized, groove means in one of the said coacting surfaces disposed on the core and armature, respectively, of such size and location that by cooperation of the groove means with the control coil and the third coil, the flux in the magnetic circuit is so dissipated that the flux decay is at substantially the same rate over all portions of said coacting surface regions, whereby said armature is caused to operate away from said core member at a substantially invariable time after each deenergization of said main coil RALPH B. IMMEL. 

